Nucleosynthetic signatures of the first stars.

The chemically most primitive stars provide constraints on the nature of the first stellar objects that formed in the Universe; elements other than hydrogen, helium and traces of lithium present within these objects were generated by nucleosynthesis in the very first stars. The relative abundances of elements in the surviving primitive stars reflect the masses of the first stars, because the pathways of nucleosynthesis are quite sensitive to stellar masses. Several models have been suggested to explain the origin of the abundance pattern of the giant star HE0107-5240, which hitherto exhibited the highest deficiency of heavy elements known. Here we report the discovery of HE1327-2326, a subgiant or main-sequence star with an iron abundance about a factor of two lower than that of HE0107-5240. Both stars show extreme overabundances of carbon and nitrogen with respect to iron, suggesting a similar origin of the abundance patterns. The unexpectedly low Li and high Sr abundances of HE1327-2326, however, challenge existing theoretical understanding: no model predicts the high Sr abundance or provides a Li depletion mechanism consistent with data available for the most metal-poor stars.

A Rare Case of Aortoenteric Graft Erosion Presenting as Candida glabrata Fungemia.

BACKGROUND: An aortoenteric fistula (AEF) describes a communication of the aorta or aortic graft with an adjacent loop of the bowel. Aortic graft erosion is a rare complication of abdominal aortic aneurysm repair. We describe a case of a patient presenting with sepsis from Candida glabrata fungemia secondary to aortoenteric erosion without any symptoms or signs of gastrointestinal bleeding. This is a unique case of Candida glabrata fungemia from aortoenteric graft erosion. Case Summary. This patient is a 75-year-old male with a history of a prior aortobifemoral bypass graft in 2005. He presented with complaints of right paraspinal pain and chills. He had no symptoms of gastrointestinal bleeding or abdominal pain. His white blood cell count was 25,600/mcl (4,000-11,000/mcL) with left shift. The erythrocyte sedimentation rate was 11 mm/hr (0-38 mm/hr), and C-reactive protein was 95.5 mg/L (<=10.0 mg/L). Blood cultures were obtained and eventually grew Candida glabrata. A computed tomography angiogram (CTA) of abdomen and pelvis demonstrated inflammation surrounding the graft concerning for graft infection with additional inflammatory changes tracking down both femoral limbs. He underwent staged bilateral femoralaxillary bypass followed by the excision of aortobifemoral bypass. CONCLUSION: Patients with aortoenteric erosion can present with sepsis in absence of gastrointestinal bleeding. Emergent computed tomography angiogram (CTA) of abdomen and pelvis should be performed to assess for aortic graft erosion or fistula. Empiric treatment with antibiotics should include antifungal agent like micafungin until the final culture is reported. The definite management is an extra anatomic bypass, followed by graft excision.

3D NLTE spectral line formation of lithium in late-type stars.

Accurately known stellar lithium abundances may be used to shed light on a variety of astrophysical phenomena such as big bang nucleosynthesis, radial migration, ages of stars and stellar clusters, and planet engulfment events. We present a grid of synthetic lithium spectra that are computed in non-local thermodynamic equilibrium (NLTE) across the stagger grid of three-dimensional (3D) hydrodynamic stellar atmosphere models. This grid covers three Li lines at 610.4, 670.8, and 812.6 nm for stellar parameters representative of FGK-type dwarfs and giants, spanning T eff = 4000-7000 K, log g = 1.5-5.0, [Formula: see text]-0.5, and A(Li) = -0.5-4.0. We find that our abundance corrections are up to 0.15 dex more negative than in previous work, due to a previously overlooked NLTE effect of blocking of UV lithium lines by background opacities, which has important implications for a wide range of science cases. We derive a new 3D NLTE solar abundance of A(Li) = 0.96 ± 0.05, which is 0.09 dex lower than the commonly used value. We make our grids of synthetic spectra and abundance corrections publicly available through the breidablik package. This package includes methods for accurately interpolating our grid to arbitrary stellar parameters through methods based on Kriging (Gaussian process regression) for line profiles, and multilayer perceptrons (a class of fully connected feedforward neural networks) for NLTE corrections and 3D NLTE abundances from equivalent widths, achieving interpolation errors of the order of 0.01 dex.

The relationship between photometric and spectroscopic oscillation amplitudes from 3D stellar atmosphere simulations.

We establish a quantitative relationship between photometric and spectroscopic detections of solar-like oscillations using ab initio, 3D, hydrodynamical numerical simulations of stellar atmospheres. We present a theoretical derivation as a proof of concept for our method. We perform realistic spectral line formation calculations to quantify the ratio between luminosity and radial velocity amplitude for two case studies: the Sun and the red giant ϵ Tau. Luminosity amplitudes are computed based on the bolometric flux predicted by 3D simulations with granulation background modelled the same way as asteroseismic observations. Radial velocity amplitudes are determined from the wavelength shift of synthesized spectral lines with methods closely resembling those used in Birmingham Solar Oscillations Network (BiSON) and Stellar Oscillations Network Group (SONG) observations. Consequently, the theoretical luminosity to radial velocity amplitude ratios are directly comparable with corresponding observations. For the Sun, we predict theoretical ratios of 21.0 and 23.7 ppm [m s-1]-1 from BiSON and SONG, respectively, in good agreement with observations 19.1 and 21.6 ppm [m s-1]-1. For ϵ Tau, we predict K2 and SONG ratios of 48.4 ppm [m s-1]-1, again in good agreement with observations 42.2 ppm [m s-1]-1, and much improved over the result from conventional empirical scaling relations that give 23.2 ppm [m s-1]-1. This study thus opens the path towards a quantitative understanding of solar-like oscillations, via detailed modelling of 3D stellar atmospheres.

Solar Surface Convection.

We review the properties of solar convection that are directly observable at the solar surface, and discuss the relevant underlying physics, concentrating mostly on a range of depths from the temperature minimum down to about 20 Mm below the visible solar surface. The properties of convection at the main energy carrying (granular) scales are tightly constrained by observations, in particular by the detailed shapes of photospheric spectral lines and the topology (time- and length-scales, flow velocities, etc.) of the up- and downflows. Current supercomputer models match these constraints very closely, which lends credence to the models, and allows robust conclusions to be drawn from analysis of the model properties. At larger scales the properties of the convective velocity field at the solar surface are strongly influenced by constraints from mass conservation, with amplitudes of larger scale horizontal motions decreasing roughly in inverse proportion to the scale of the motion. To a large extent, the apparent presence of distinct (meso- and supergranulation) scales is a result of the folding of this spectrum with the effective "filters" corresponding to various observational techniques. Convective motions on successively larger scales advect patterns created by convection on smaller scales; this includes patterns of magnetic field, which thus have an approximately self-similar structure at scales larger than granulation. Radiative-hydrodynamical simulations of solar surface convection can be used as 2D/3D time-dependent models of the solar atmosphere to predict the emergent spectrum. In general, the resulting detailed spectral line profiles agree spectacularly well with observations without invoking any micro- and macroturbulence parameters due to the presence of convective velocities and atmosphere inhomogeneities. One of the most noteworthy results has been a significant reduction in recent years in the derived solar C, N, and O abundances with far-reaching consequences, not the least for helioseismology. Convection in the solar surface layers is also of great importance for helioseismology in other ways; excitation of the wave spectrum occurs primarily in these layers, and convection influences the size of global wave cavity and, hence, the mode frequencies. On local scales convection modulates wave propagation, and supercomputer convection simulations may thus be used to test and calibrate local helioseismic methods. We also discuss the importance of near solar surface convection for the structure and evolution of magnetic patterns: faculae, pores, and sunspots, and briefly address the question of the importance or not of local dynamo action near the solar surface. Finally, we discuss the importance of near solar surface convection as a driver for chromospheric and coronal heating. ELECTRONIC SUPPLEMENTARY MATERIAL: Supplementary material is available for this article at 10.12942/lrsp-2009-2.